MULE-6833: GZip transformer failing

GZipCompressTransformer serializes objects (e.g. Strings) into byte arrays before compressing. Its counterpart, the GZipUncompressTransformer receives a byte array, decompresses it and only deserializes back into an object if the return class is explicitely set on the transformer. Now the GZipUncompressTransformer tries to "guess" if the decompressed byte array was serialized by trying to deserialize it and checking if it failed. If the deserialization was successful it returns the resulting object, otherwise, it returns the decompressed byte array.

MULE-6833: GZip transformer failing

- Added missing license header.
(cherry picked from commit 99b7507eaddc16847dc9dd8b65c6808b39a0c26b)

Conflicts:
	core/src/main/java/org/mule/transformer/compression/GZipUncompressTransformer.java
	core/src/test/java/org/mule/transformer/compression/GZipTransformerStreamTestCase.java
(cherry picked from commit d51d730d484019a0ae688fd2f022aff55f9f45a4)

MULE-6833: GZip transformer failing

- Fixed failing test.
(cherry picked from commit b7ce14f16a12c4f28ad84b9a67667551e8cb36eb)
(cherry picked from commit 0033361d0966cd7aa45d679fccee13eb7ce75d8c)
(cherry picked from commit 56714fe319a7f97c199a6f0a72cace1d12889c4a)